Why are some people healthy and others not? It seems a simple question. The answers, however, are complex and have to do not only with disease and illness, but also with who we are, where we live and work, and the social and economic policies of our government, all of which play a role in determining our health.
Institute of Medicine. The Future of the Public’s Health in the 21st Century, 2003.
In recent years, attempts to determine why some people are healthy while others experience pain and illness most often have focused on the biological aspects of health. Biomedical research has contributed enormously to our knowledge of disease and to the development of new medical technologies and clinical and pharmaceutical interventions that improve the lives of so many. Most recently, the mapping of the human genome has uncovered new information about the association of genomics with disease. As Guttmacher and Collins have noted, “Genomics, which has quickly emerged as the central basic science of biomedical research, is poised to take center stage in clinical medicine as well” (Guttmacher and Collins, 2004).
Yet, over the years a large body of evidence also emerged that indicates that “almost half of all causes of mortality in the United States are linked to social and behavioral factors such as smoking, diet, alcohol use, sedentary life-style, and accidents” (IOM, 2000). Few diseases or conditions are caused purely by genetic factors; most are the result of interactions between genetic and environmental factors. Therefore, in order to continue to expand our knowledge of how to improve the health of individuals and populations, it becomes imperative to conduct research that explores how the interactions among social, behavioral, and genetic factors affect health. As a result, many are now engaged in attempts to determine how best to integrate research priorities to include a greater focus on these factors.
The National Institutes of Health (NIH), Office of Behavioral and Social Sciences Research, in conjunction with the National Human Genome
Research Institute and the National Institute of General Medical Sciences requested that the Institute of Medicine (IOM) undertake a study to examine the state of the science on gene-environment interactions that affect human health, with a focus on the social environment.1 The study was to identify approaches and strategies to strengthen the integration of social, behavioral, and genetic research and to consider the relevant training and infrastructure needs. More specifically, the study was to:
Review the state of the science on the interactions between the social environment and genetics that affect human health.
Develop case studies that will demonstrate how the interactions of the social environment and genetics affect health outcomes; illustrate the methodological issues involved in measuring the interactions; elucidate the research gaps; point to key areas necessary for integrating social, behavioral, and genetic research; and suggest mechanisms for overcoming barriers.
Identify gaps in the knowledge and barriers that exist to integrating social, behavioral, and genetic research in this area.
Recommend specific short- and long-term priorities for social and behavioral research on gene-social environment interactions; identify mechanisms that can be used to encourage interdisciplinary research in this area.
Assess workforce, resource, and infrastructure needs and make actionable recommendations on overcoming barriers and developing mechanisms to accelerate progress.
In response to the NIH request, IOM established the Committee on Assessing Interactions Among Social, Behavioral, and Genetic Factors in Health. (See Appendix A for a discussion of committee methodology and Appendix G for biographical sketches of committee members.)
Assessing the impact on health of interactions among social, behavioral, and genetic factors is an emerging and complex field. Much remains to be learned about how these factors interact to impact health, including the most basic concept of defining interaction and how it can be characterized. Because there is a need for greater etiological understanding in order to identify future clinical research or develop effective interventions aimed at improving health outcomes, the committee has focused its efforts and this report on etiological research.
Of primary importance to the work of the committee was the recogni-
tion that multiple determinants contribute to the health of individuals and populations. Furthermore, the committee emphasized the development of a common understanding of concepts and terms crucial to advancing our understanding of the interaction of multiple determinants of health.
The definition of health has evolved over time, as has its measurement. Because health cannot be measured directly, a number of variables have been used as indicators of the concept of health. Prior to the mid-1900s, negative indicators such as mortality and disease rates were used—with the idea that the lower the rate, the healthier the population. Mortality or disease rates continue to be used as broad indicators when comparing populations—such as infant mortality rates or rates of specific diseases. However, a view of health as something much broader than the mere absence of disease has led to an evolution in thinking about the framework for health determinants.
One such framework was developed by Lalonde (1974) and includes environment, lifestyle, human biology, medical care, and health care organization as major determinants of health. The Lalonde framework recognized the importance of individual risk factors to health and led to further analysis and exploration of these factors’ impact on health. A more complex model developed by Evans and Stoddart (1990) suggested a new framework for health determinants:
It should accommodate distinctions among disease, as defined and treated by the health care system, health and functioning, as perceived and experienced by individuals, and well-being, a still broader concept to which health is an important but not the only, contributor. It should … permit and encourage a more subtle and more complex consideration of both behavioural and biological responses to social and physical environments.
Since the work of Evans and Stoddart, a number of models of health determinants have been developed. A 1999 IOM report explored core concepts of health, proposing a model of determinants that illustrated how individual characteristics (biology and life course, lifestyle and health behavior, illness behavior, personality and motivation, and values and preferences) and environmental characteristics (social and cultural, economic and political, physical and geographic, and health and social care) influence health-related quality of life (symptoms, functional status, health perceptions, and opportunity) (IOM, 1999).
Kaplan and colleagues (2000) proposed a framework that “builds bridges between levels rather than attributing primary importance to one
level or another.” Their multilevel approach to health determinants includes pathophysiological pathways, genetic/constitutional factors, individual risk factors, social relationships, living conditions, neighborhoods and communities, institutions, and social and economic policies as the major forces that affect health. The Future of the Public’s Health (IOM, 2003a) and Who Will Keep the Public Healthy? (IOM, 2003b) emphasized that improving the health of populations requires understanding the ecology of health and the interconnectedness of the biological, behavioral, physical, and socioenvironmental spheres.
For the purposes of developing this report, the committee has focused its examination and analysis of factors on three major domains: social factors, behavioral factors, and genetic factors. Furthermore, the committee found it most useful to embrace a model that includes multiple determinants of health that are related and linked in many ways. Such a model is frequently referred to as an ecological model, because it emphasizes the linkages and relationships among multiple factors (or determinants) affecting health. As noted by IOM (2003b):
An ecological model assumes that health and well-being are affected by interaction among multiple determinants including biology, behavior, and the environment. Interaction unfolds over the life course of individuals, families, and communities, and evidence is emerging that societal-level factors are critical to understanding and improving the health of the public.
An ecological model, therefore, provides the appropriate framework for assessing the impact on health of interactions among social, behavioral, and genetic factors.
Despite the fact that a complex interplay of factors influences vulnerability and resistance to disease, “the vast majority of the nation’s health research resources have been directed toward biomedical research endeavors” (IOM, 2000). However, recent studies suggest that research on interactions of genetics with social-environmental factors is essential to understanding health and illness. For example, Caspi and colleagues (2003) found “evidence of a gene-by-environment interaction, in which an individual’s response to environmental insults is moderated by his or her genetic makeup.” In another study, Manuck et al. (2005) found that the socioeconomic status of communities is associated with variations in central nervous system serotonergic responsivity, which may have implications on the prevalence of psychological disorders and behaviors such as depression, impulsive aggression, and suicide.
Various pathway diagrams have been developed to represent the many ways in which social, behavioral, and genetic factors influence health. How-
ever, it is the committee’s hope that, no matter which model one chooses, the discussion and recommendations set forth in this report will facilitate efforts to examine the interaction of multiple determinants on health, with a specific emphasis upon the interaction of the social environment and behavior with the genome.
To conduct research on interactions requires a shift in focus from research that is dominated by single disciplines—even when their work is complementary—to transdisciplinary research. “Transdisciplinary research involves broadly constituted teams of researchers that work across disciplines in the development of the research questions to be addressed” (IOM, 2003b). While interdisciplinary research focuses on answering a question of mutual concern to those of various disciplines, and multidisciplinary research involves research on questions of both mutual and separate interest to participating investigators, transdisciplinary research “implies the conception of research questions that transcend the individual departments or specialized knowledge bases because they are intended to solve … research questions that are, by definition, beyond the purview of the individual disciplines” (IOM, 2003b). Transdisciplinary research calls for the various disciplines involved to work together as a team to define the nature of the problem to be resolved. As stated in the above mentioned IOM report (2003b):
The practical ramifications of such an approach are that the disciplines will no longer function like “silos” that exist side-by-side, deeply rooted in their respective traditions. Rather, these disciplines will involve more broadly constituted and integrated “teams.”
In other words, in transdisciplinary research all of the disciplines involved are forced to change the ways in which they think about the problem, which in turn requires a transformation in the training of a cadre of new investigators, as well as new training for experienced investigators. Making this shift may be the most difficult challenge that is involved in studying the interaction of the genome and the social environment.
Developing teams of scientists who can engage in and conduct the necessary transdisciplinary research presents several practical difficulties. For example, researchers from different disciplines must be able to understand and value one another’s language, concepts, and methods. Additionally, sources of data that support such transdisciplinary efforts must be developed or enhanced. Nowhere are the difficulties of transdisciplinary research better illustrated than when attempting to develop research efforts
that addresses the impact of interactions among social, behavioral, and genetic factors. Such research could include research scientists from the fields of anthropology, sociology, psychology, genetics, molecular biology, biostatistics, and epidemiology.
Unfortunately, barriers to conducting effective transdisciplinary research exist within the institutions that prepare researchers, which are, for the most part, organized along single discipline departmental lines. In this system, promotion and rewards within the institution flow from the departments, each of which tends to value most highly the research and teaching that is conducted within its particular sphere. In addition, faculty members within these institutions do not have the knowledge and skills that are needed to engage in transdisciplinary research or teaching. Even when the results from such research emerge, there are not enough “peers” available to evaluate those results because most scientists and reviewers, while firmly grounded in their respective disciplines, are not sufficiently grounded in the other disciplines that may be involved in the research.
The report by the National Academy of Sciences/National Academy of Engineering/Institute of Medicine Facilitating Interdisciplinary Research (NAS/NAE/IOM, 2004) outlines several changes that are needed to foster interdisciplinary research, many of which also could be applied to attempts to facilitate transdisciplinary research, such as overcoming institutional barriers related to policies that govern hiring, promotion, tenure, and resource allocation. Furthermore, that report suggests that much can be learned from industry and national laboratories that organize research efforts around the problems they wish to address rather than by discipline. (See Appendix B for a complete list of recommendations from the report on interdisciplinary research.)
The committee commissioned papers to examine areas that might prove fruitful for investigation of the impact on health of the interaction among social, behavioral, and genetic factors. In the paper on obesity (see Appendix C), Myles S. Faith and Tanya V.E. Kral present evidence that genetic and social-environmental factors promote obesity through their independent influences on intermediary behavioral variables. Robert J. Thompson, Jr., in his study of sickle cell anemia (a Mendelian single-gene disorder) found that the severity of the symptoms of this disease is influenced by social and behavioral factors. He found that stress (primary related to dealing with daily hassles) and stress processing (primarily in relation to cognitive appraisals and attributions, coping methods, and family support) is associated with variability in the manifestation of sickle cell disease (see Appendix D). The paper on interactions prepared by Sharon Schwartz
(Appendix E) explores new ways of thinking about biologic interaction. A paper on immunology prepared by Steve W. Cole discusses what is known about the interaction between genes and the social environment in the context of immune system function.
Each of these papers, as well as additional analysis and synthesis of information conducted by committee members, points to the need for research on the interactions among social, behavioral, and genetic factors and their impact on health.
In its charge to the committee, NIH sponsors defined social environment as the relations among people as both individuals and in societies. The term was not defined in a way that included environmental conditions such as global warming and toxic waste, even if they result from human activities. The committee has chosen to emphasize certain variables of the social environment as having high potential for research about interactions, both because there is a large body of evidence that examines the impact of these variables on health and because there exist well-established and well-accepted measures for the investigation of these variables. These variables are socioeconomic status, race/ethnicity, social networks/social support, and the psychosocial work environment. Furthermore, the committee determined that the life course perspective is crucial when studying interactions because, as stated in Chapter 2, “the influence of social and cultural variables on health involves dimensions of both time (critical stages in the life course and the effects of cumulative exposure) as well as place (multiple levels of exposure).” Chapter 2 explores the impact of the social and cultural environment on health, providing definitions, examining what we know about the influences of these factors on health, and identifying the limitations of current research.
Genetic factors and their impact on health are examined in Chapter 3, which focuses on what is known or theorized about the direct link between genes and health and what still must be explored to understand the environmental interactions and relative roles among genes that contribute to health and illness. This chapter describes simple Mendelian patterns of disease inheritance and also explores genetic susceptibility to disease as the consequence of the joint effects of many genes, each with small to moderate effects and often with interaction among themselves and the environment that give rise to the distribution of disease risk that is seen in a population. It also includes a discussion of epigenetic phenomenon, mechanisms of gene expression and regulation, aspects of health influenced by genetics, and the limitations of current research on the interactions of genetic factors with social and behavioral factors.
The impact of behavioral factors on health is explored in Chapter 4. The term behavior includes two components. First are observable behaviors that influence health, including smoking, drinking, drug use, diet, and exercise. Such factors are frequently referred to as risk factors. The second component includes certain psychological characteristics, including cognitive and emotional function and resilience. The discussion of behavioral and psychological states includes an examination of stress and coping, and it identifies the limits of current research on the interactions of behavioral factors with genetics and social factors.
The search for a better understanding of genetic and environmental interactions as determinants of health has revealed some fundamental yet complex aspects, or traits, of human identity that pose a challenge to researchers, but also provide an opportunity for clarification. Chapter 5 discusses two such complex traits: sex/gender and race/ethnicity. These traits are particularly useful and important because they have clear social dimensions that need to be taken into account in order to understand their impact on health, and each has genetic underpinnings to varying degrees. As discussed earlier, the committee believes that research on the impact of interactions among social, behavioral, and genetic factors on health must be conducted from a life course perspective:
As a concept, a life course is defined as “a sequence of socially defined events and roles that the individual enacts over time” (Giele and Elder, 1998).
These events and roles do not necessarily proceed in a given sequence, but rather constitute the sum total of the person’s actual experience. Thus the concept of life course implies age-differentiated social phenomena distinct from uniform life-cycle states and the life span (Families.com, 2003).
Chapter 6 discusses how future research needs to reflect the integrated nature of the social and physical environment and gene function that is the salient feature of biological systems, describing the variety of models needed in light of the fact that rarely is there a one-to-one relationship between genes and a trait.
The use of animal models for understanding interactions is explored in Chapter 7, which describes what can be learned from animal models about how social systems regulate physiological systems and gene functions, presents criteria for the conduct of animal models, and describes the limitations of and power for generalizations from animal studies.
Chapter 8 explores research design and analysis approaches for the study of interactions. This chapter defines types of interactions, provides an example of the systems or pathways through which the social environment
affects health—including behavioral, physiological, cellular, and genetic paths—and discusses models through which genes and the social environment could affect health. It also describes a progression of studies that could be used to study each of these models and discusses statistical issues related to testing gene-environment interactions.
Chapter 9 addresses infrastructure needs. It examines three aspects of infrastructure: education, data, and incentives and rewards. The discussion explores ways in which existing mechanisms can be focused to strengthen the infrastructure and also examines potential new mechanisms that could be developed.
Chapter 10 addresses ethical and social implications, focusing on such factors as the need for transparency in research and exploring the level of general public understanding of research on interactions, the disclosure of research results to participants, the social meaning of the research that is conducted, and the challenges of data privacy and availability. Chapter 11, the final chapter, briefly summarizes the main points of the study and presents the conclusions of the report.
The primary goals of this report are to provide a research framework for assessing the impact of interactions among social, behavioral, and genetic factors on health, to identify and make recommendations about infrastructure needs and options, and to emphasize the importance of integrating the ethical and social implications into all research involving these interactions.
Research assessing the impact of interactions among social, behavioral, and genetic factors on health holds great promise for helping explicate some of the complex relationships between health outcomes and the myriad multiple determinants of health. The findings of such research may well assist us in devising interventions that will benefit both individuals and the larger populations and groups within society.
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